Cardiac arrest, exposure to high voltage power lines and other trauma to the body can result in heart fibrillation which is the rapid and uncoordinated contraction of the cardiac muscle. The use of external defibrillators to restore the heartbeat to its normal pace through the application of an electrical shock is a well recognized and important tool for resuscitating patients. External defibrillation is typically used in emergency settings in which the patient is either unconscious or otherwise unable to communicate.
Automated external defibrillators or AEDs are used by police officers, paramedics and other first-responder emergency medical technicians to resuscitate cardiac arrest patients. It is important that the AEDs carried by these technicians be continuously operational and ready for use on a moment's notice. It is essential that in a high stress situation of cardiac arrest, the technician be able to rely on the operability of the AED. Studies have shown that the chances of successfully resuscitating patient decreases approximately ten percent per minute following cardiac arrest. Thus, it is essential that the AED provide an audible alarm to a user when a malfunction or problem with the AED is detected so that the AED may be repaired before its use is required.
Alarm circuits have been known for quite some time now. In many existing devices, alarm circuits may be activated by a watch dog timer or a microprocessor. In some known systems, in order for the alarm circuit to operate, the circuit's real time clock must be continuously operational. Moreover, substantial amounts of additional circuitry are required for the alarm system to operate. In some systems, the alarm circuit is designed to produce an audible alarm at a desired frequency. Each time an audible tone is desired, the circuitry is, in effect, powered up. For devices utilizing batteries having a fixed life, this is a drain on the non-recoverable battery life. There is, therefore, a need for an audible alarm circuit that is capable of producing an audible alarm when initiated by a processor but that may however, run independently of the processor thereafter thereby reducing drain on internal batteries.